Molecular methods employing the polymerase chain reaction (PCR) were developed to identify a panel of 30 important bacterial, viral and fungal pathogens of animals. This capability has proven to be a valuable adjunct to traditional microbiological techniques especially for detecting microbes difficult to culture or those buried in archival material. Development of these procedures has also provided a means for correlating pathogen load with the animal's age and the course of disease. The efficacy of many of these techniques is still being evaluated.